Recently, a memory card having a memory chip as a recording medium for recording information is used. Such a memory card is excellent in portability, and widely used as a recording medium for portable electronic equipment such as a portable information terminal and a portable telephone. And, portable electronic equipment is increasingly reduced in size and thickness in recent years from the viewpoint of improved portability, and in this respect, it is required to reduce the size and thickness of the memory card.
In order to meet the requirement, in the manufacture of a memory card, a gold wire or the like is used for wire bonding of an electrode on a memory chip and an electrode on a circuit board for the purpose of connection and mounting thereof. Specifically, for example, another memory chip is first laminated in a position a little shifted on a memory chip bonded to a lead frame by using an adhesive agent or double-side adhesive tape. Subsequently, the electrode of a control chip bonded on the lead-frame and the electrode of two memory chips is connected to the lead frame via a gold wire. A technology for reducing the thickness of a memory card in this way is disclosed (for example, see Patent Document 1).
Also available is a method of flip-chip mounting a memory chip or control chip on a circuit board via a resin material.
However, as shown in the memory card of Patent Document 1, a memory chip and control chip are generally formed from a silicon material, and a circuit board is formed from glass epoxy resin in many cases. And, since glass epoxy resin is greater in thermal expansion coefficient than silicon, when the temperature on a bonding process decreases to the normal temperature, the circuit board shrinks more than the memory chip. However, such shrinking is suppressed on the mounting surface because a memory chip is bonded to the mounting surface of the circuit board. As a result, the circuit board flexes in a convex shape toward the mounting surface side of the memory chip, equivalently increasing in thickness of the circuit board, causing a problem to arise against the reduction in thickness of the memory card. Such flexing of the circuit board is more remarkable when the bonding temperature is higher because the temperatures of the circuit board and the memory chip are lowered to the normal temperature after the memory chip is bonded to a flat circuit board in a state of being heated, for example, by using a thermal press-fitting method. That is, when the difference between the temperature in bonding the circuit board and memory chip and the normal temperature is greater, the flexing amount of the circuit board becomes larger.
Further, a memory chip is bonded to a circuit board via adhesive agent, the circuit board sometimes flexes in a convex shape toward the mounting surface side due to shrinking of the adhesive agent coagulated. The cause of this is the difference in rigidity between memory chip and circuit board, and there arises greater influence in a circuit board being less in rigidity.
Also, since shrinking at the mounting surface side of the circuit board is suppressed by the memory chip, there exist a great stress in the electrode that is a bonding portion. As a result, there is a problem of reliability because the lowering of bonding strength or peeling is liable to take place depending upon the heat history or external load under the using environment.
As described above, there are important problems such as the generation of flexure of a memory card and lowering of the connection reliability due to the difference in thermal expansion coefficient and shrinkage between memory chip, circuit board and adhesive agent.    Patent Document 1 Unexamined Japanese Patent Publication 2004-13738